1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device in which the semiconductor devices are processed in a state of charging a plurality of substrates on a boat.
2. Description of the Related Art
When a reactive gas, such as SiH2Cl2 (DCS: dichlorosilane) and NH3 gas, for instance, is supplied into a brand-new semiconductor device manufacturing apparatus which has been just delivered to a user to form a Si3N4 film on a wafer, a detected amount of Fe contamination on the wafer comes to 10 to 30 times of the permissible value (10xc3x971010 atoms/cm2). This is due to initial metal contamination. The source of the initial metal contamination is due to a residue containing Fe, which comes from corrosion on the surface of metal parts of a furnace port of the apparatus or remains in a supply system. Yield of the semiconductor device which is produced with a wafer exposed to a contamination amount over the permissible value comes to remarkably low. Therefore, it is necessary to suppress the amount of contamination below the permissible value. It has been known from practical experience that repeated deposition decreases the initial metal contamination gradually. Accordingly, a method of repeating the deposition 30 to 40 times until the amount of the metal contamination reaches equal to or less than the permissible value has been adopted generally in order to decrease the initial metal contamination.
However, the above-described method to repeat the deposition requires to continue the deposition repeatedly for three to four weeks from start of the method till the amount of metal contamination reaches equal to or below the permissible value. Thus, it is difficult to decrease the metal contamination in a short time, and the semiconductor device manufacturing apparatus cannot be used during that time for manufacturing semiconductor device. Therefore, various methods to decrease the metal contamination at the furnace port have been proposed.
In a patent document 1, in order to prevent generation of metal impurities by the surface of metal parts (manifold) being exposed to NH3 in a heat treatment apparatus using NH3, a method to form an oxide film on the surface of metal parts is proposed. In order to form the oxide film, O2 is supplied from an O2 gas supply port and the heat treatment is carried out in an O2 gas atmosphere.
In a patent document 2, a method is disclosed in that a passivation treatment (forming of a chromium oxide film) is applied to a metal substance (SUS flange) in a CVD apparatus so that the metal substance changes to be inactive to a corrosive gas and a reducing gas, and a coating film is formed further thereon to prevent the metal contamination.o In order to form a chromium oxide film, the surface of the metal parts made of SUS is smoothed by electropolishing and the like and then the SUS part is washed with heated deionized water. The film deposited on the chromium oxide film is a CVD film. As the sort of film (raw materials), a Poly-Si film (SiH4/N2), a Si3N4 film (DCS/NH3/N2), a SiC film (SiH4/CH4/N2), and a SiO2 film (TEOS/N2) can be used. The thickness of the coating film is about 100 nm.
In a patent document 3, a method of coating metal parts with a chromic oxide film to suppress corrosion and metal contamination on the metal parts in an oxidation apparatus and a CVD apparatus is disclosed. In order to apply coating, a slurry is coated on a metal surface, then a porous film is formed by heating, which is impregnated with an aqueous solution of chromium acid anhydride while being heated. This combination of impregnation of chromium acid and heat treatment is repeated. Incidentally, there is also a description that a cycle purge is carried out after a wafer is loaded and before it is treated. The timing of the cycle purge is after the wafer loading and before the wafer treatment.
In a patent document 4, a method is disclosed in that in a CVD apparatus depositing a SiN film, the inside of a reaction tube is coated with the same film as the film to be deposited in order to prevent contamination by impurities of heavy metals and the like generated from a reaction tube, not from metal members. When coating, a reactive gas is supplied in an amount equal to or more than the amount supplied during the deposition. The thickness of the coating film is equal to or more than 0.8 xcexcm, or equal to or more than 1 xcexcm.
In a patent document 5, in a CVD apparatus, a method of covering at least exposed portions of a flange portion and a lid body (metal members) in the inside of a reaction tube with an adherent layer (ceramics, quartz glass, SiC, and so on) of non-metal material is disclosed. The kinds of film (raw materials) deposited by the CVD apparatus is SiO2(SiH4/O2), and Si(DCS/H2).
The patent document 1: Japanese Patent Laid-open No. Hei 11-26441
The patent document 2: Japanese Patent Laid-open No. Hei 11-345772
The patent document 3: Japanese Patent Laid-open No. 2002-222807
The patent document 4: Japanese Patent Laid-open No. Hei 9-246256
The patent document 5: Japanese Patent Laid-open No. Hei 2-174225
However, in all of the inventions in the above-described patent documents 1 to 5, since the methods of decreasing the metal contamination are complicated and not enough in lowering a metal contamination level, there is room for improvement. That is, there are the following disadvantages respectively in (1) the method of decreasing the metal contamination by growing an oxide film as described in the patent document 1 and 2, (2) the method of decreasing the metal contamination by cycle purge as described in the patent document 2, and (3) the method of decreasing the metal contamination by coating as described in the patent document 2 to 5.
(1) In the method of decreasing the metal contamination by growing an oxide film, the invention described in the patent document 1 requires a new O2 gas supply port, which makes the structure complicated, and the invention described in the patent document 2 requires polishing and washing of the SUS parts, which makes the steps complicated.
(2) In the method of decreasing the metal contamination by cycle purge, in the invention described in the patent document 3, the cycle purge is performed after the wafer load and before the wafer processing (deposition), which takes too much time till the deposition starts.
(3) In the method of reducing the metal contamination by coating, the invention described in the patent document 2 required the coating on the chromium oxide film. The coating film has a similar composition to the kind of film deposited in the CVD process, but not the same composition, which makes the steps complicated. Further, in the invention described in the patent document 3, the coating film is a chromium oxide film and in order to form the chromium oxide film, slurry is applied and heated, and then, an aqueous solution of chromium acid anhydride is impregnated and heat-treated. Repetition of the chromium impregnation and the heat-treatment is required, which makes the steps complicated. In the invention described in the patent document 4, the same film as the deposited film is applied on the inside surface of the reaction tube by coating, but since the number of the coating is only one time, reduction of the metal contamination is not enough. Furthermore, since a reactive gas in an amount equal to or more than that at the time of deposition is supplied to perform the coating without loading wafers in the inside of the reaction tube, the film more than required is formed in the inside of the reaction tube, which causes fears of generating particles due to peeling-off of the film. Further, the invention described in the patent document 5 requires to coat with a non-metal film different from the kind of film used for deposition, which makes the steps complicated.
An object of the present invention is to provide a method for manufacturing a semiconductor device, which solves problems in the related art described above, and is capable of reducing a metal contamination level sufficiently in spite of its simple structure.
A first invention relates to a method for manufacturing a semiconductor device to perform processing of substrates charged on a boat into a reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and a furnace port located below the heater and including the metal parts which support the reaction tube, and the method for manufacturing the semiconductor device comprising the step of: coating the surface of the metal parts of the furnace port of the reaction furnace with a film, by supplying the same gas to be used for substrate processing into the reaction furnace, before substrate processing, wherein the coating step is performed a plurality of times. With increase of the number of times in the repeat of the coating process, the metal contamination level is lowered. Further, since the same gas as that used for substrate processing is allowed to pass in the reaction furnace, a gas supply system for coating and a gas supply system for substrate processing can be commonly used.
A second invention is characterized in that in the method for manufacturing the semiconductor device in the first invention, a silicon nitride film is formed on the substrates by a CVD method using SiH2Cl2 and NH3 in the substrate processing step; and wherein at least SiH2Cl2 is supplied into the reaction furnace in the coating step. When the SiN film is formed using SiH2Cl2 and NH3, metal contamination is especially a matter of concern, and can be improved by the invention.
A third invention is characterized in that in the second invention, the film used to coat the surface of the metal parts is a SiO2 film. Deposition of SiO2 on the surface of the metal parts is more effective for the reduction of metal contamination than merely oxidizing the surface of the metal parts to grow the oxide film on the surface of the metal parts.
A fourth invention is characterized in that in the third invention, the SiO2 film is formed by reaction of oxygen containing substance such as H2O coming into the furnace with SiH2Cl2 supplied to the reaction furnace. An oxygen containing gas support system to form the SiO2 film becomes unnecessary.
A fifth invention is characterized in that in the first invention, the coating steps comprises the steps of: loading substrates charged on the boat which will not be final products, into the reaction furnace; supplying gas used for the substrate processing into the reaction furnace while heating the substrates charged on the boat in the reaction furnace; and unloading the substrates charged on the boat from the reaction furnace. Since the coating step is carried out when the substrates are charged on the boat, it is possible to prevent formation of a film thicker than required on quartz parts of the reaction tube and the like.
A sixth invention is characterized in that in the first invention, the amount of gas supplied in the coating step is calculated to be greater than the amount of gas supplied in the substrate processing step, which allows the film to be quickly deposited on the surface of the metal parts. Further, it is possible to discharge residual components remaining inside the gas supply system.
A seventh invention is characterized in that in the first invention, the time to keep supplying the gas in the coating step is made longer than the time to keep supplying the gas in the substrate processing step. When the time to supply the gas is made longer, a film of required thickness can be deposited on the surface of the metal parts. Further, it is possible to change metal contaminants in the reaction furnace into chlorides so as to discharge them more effectively.
An eighth invention is characterized in that in the first invention, every time the coating step is repeated, the substrates are replaced by new substrates which will not be final products. Every time the coating step is repeated, the substrates are replaced by new substrates, which prevents the film from peeling off of the substrate.
A ninth invention relates to a method for manufacturing a semiconductor device to deposit a silicon nitride film on substrates charged on a boat by supplying SiH2Cl2 and NH3 as deposition gases into a reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and a furnace port located below the heater and including the metal parts which support the reaction tube, and the method for manufacturing the semiconductor device comprising the steps of: coating with a SiO2 film on the surface of metal parts of the furnace port of the reaction furnace by supplying at least SiH2Cl2 which is a deposition gas into the reaction furnace, before deposition so as to react with oxide containing substance coming into the furnace. It is possible to form a SiO2 film easily on the surface of the metal parts, which has much better effect in reduction of metal contamination than an oxide film by letting the SiH2Cl2 react with the oxygen containing substance.
A tenth invention relates to a method for manufacturing a semiconductor device to perform processing of substrates charged on a boat into the reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and the furnace port located below the heater and including the metal parts which support the reaction tube, and the method for manufacturing the semiconductor device comprising the steps of: coating the surface of metal parts with a film by supplying gas to be used for substrate processing into the reaction furnace, before the substrate processing; wherein the coating step comprises: loading the substrates charged on the boat, which will not be final products, into the reaction furnace; supplying gas used for the substrate processing into the reaction furnace while heating the substrates charged on the boat in the reaction furnace; and processing the substrates charged on the boat in the reaction furnace, unloading the substrates charged on the boat from the reaction furnace. Since the coating step is performed in a state of charging substrates on the boat, it is possible to prevent formation of a film thicker than required on a quartz part of the reaction tube and the like.
An eleventh invention relates to a method for manufacturing a semiconductor device to perform processing of substrates charged on a boat in the reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and the furnace port located below the heater and including the metal parts which support the reaction tube, and the method for manufacturing the semiconductor device comprises the step of: growing an oxide film on the surface of metal parts of a furnace port before the substrate processing, wherein the step of growing the oxide film comprises the steps of: loading the substrates charged on the boat, which will not be final products, into the reaction furnace; heating the substrates charged on the boat in the reaction furnace; and unloading the substrates charged on the boat from the reaction furnace under the atmospheric condition. Since the oxide film is grown on the surface of the metal parts of the furnace port before the substrate processing, the surface of the metal parts of the furnace port is covered with the oxide film so that reduction of the amount of metal contamination from the furnace port can be promoted. Further, since the substrate charged on the boat is unloaded from the reaction furnace under the atmospheric condition, it is possible to grow the oxide film on the surface of metal parts of the furnace port due to radiant heat from the heater inside the reaction furnace, radiant heat from heated substrate and oxygen under the atmospheric condition.
A twelfth invention is characterized in that in the eleventh invention, the oxide film growing step is repeated a plurality of times before the substrate processing step. Since the substrates charged on the boat are unloaded from the reaction furnace a plurality of times under the atmospheric condition, it is possible to grow further the oxide film on the surface of the metal parts of the furnace port due to radiant heat from the heater inside the reaction furnace, radiant heat from heated substrate and oxygen under the atmospheric condition.
A thirteenth invention is characterized in that in the eleventh invention, the oxide film growing step is performed while supplying an inert gas from a gas supply system into the reaction furnace. When the oxide film growing step is performed while supplying the inert gas into the reaction furnace from the gas supply system, it is possible to discharge more effectively residual components such as moisture, particles and so on which remain in the inside of the gas supply system.
A fourteenth invention relates to a method for manufacturing a semiconductor device to perform processing of substrates charged on a boat in the reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and the furnace port located below the heater and including the metal parts which support the reaction tube, and the method for manufacturing the semiconductor device comprises the step of: growing an oxide film on the surface of metal parts of a furnace port before the substrate processing, wherein the step of growing the oxide film comprises the steps of: inserting the boat into the reaction furnace without charging the substrates thereon; maintaining a furnace port cap which supports the boat and blocks an opening of the furnace port (opening of the reaction furnace) to be apart from the opening of the furnace port; and heating the inside of the reaction furnace in a state of keeping the furnace port cap apart from the opening of the furnace port. Since heating the inside of the reaction furnace is performed in a state that the furnace port cap is kept apart from the opening of the furnace port without blocking the opening of the furnace port completely, though the boat is inserted into the reaction furnace without charging substrates on the boat, it is possible to deposit the oxide film on the surface of the cap portion which is metal parts of the furnace port due to direct radiant heat from the heat of the furnace, and oxygen in the atmosphere coming from a gap between the furnace port cap and a furnace port flange. Therefore, reduction of the amount of the metal contamination from the furnace port can be promoted.
A fifteenth invention is characterized in that in the fourteenth invention, the furnace port cap is kept apart from the opening of the furnace port by about 20 mm. When the distance of the alienation is smaller than the distance of about 20 mm, inflow of oxygen in the atmosphere is little, and when it is larger than the distance of about 20 mm, the amount of escape of the radiant heat becomes large. Therefore, the distance of about 20 mm is just well-balanced between the amount of inflow of oxygen and the amount of escape of the radiant heat, so that the oxide film can be grown effectively on the surface of the cap portion which is metal parts of the furnace port.
A sixteenth invention is characterized in that in the fourteenth invention, the oxide film growing step is performed while supplying an inert gas from a gas supply system into the reaction furnace. When the step of growing the oxide film is performed while supplying the inert gas from the supply system into the reaction furnace, it is possible to discharge more effectively residual components such as moisture, particles and so on which remain in the inside of the gas supply system.
A seventeenth invention relates to a method for manufacturing a semiconductor device to perform processing of substrates charged on a boat in a reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and a furnace port located below the heater and including metal parts which support the reaction tube, the method for manufacturing the semiconductor device comprises the steps of: growing an oxide film on the surface of metal parts of the furnace port before the substrate processing; and coating with a film on the surface of metal parts by supplying gas to be used for the substrate processing, in the reaction furnace, wherein the coating step is performed a plurality of times. Oxidation on the surface of the metal parts before the coating step improves further the preventive effect of the metal contamination.
An eighteenth invention is characterized in that in the seventeenth invention, included is a step of cycle purging the inside of the reaction furnace after the step of growing the oxide film and before the step of coating. When the step of cycle purging the inside of the reaction furnace is included after the step of growing the oxide film and before the step of coating, it is possible to reduce the amount of the metal contamination more quickly. That is, when a residue which includes metals remaining in the inside of the reaction furnace is discharged by the cycle purge, it is possible to coat a film with no residue contained on the oxide film formed by the step of growing the oxide film.
A nineteenth invention is characterized in that in the seventeenth invention, included is a step of cycle purge in the reaction furnace after the step of coating. Even when the step of cycle purge in the reaction furnace after the step of coating is included, it is possible to reduce the amount of the metal contamination quickly.
A twentieth invention relates to a substrate processing apparatus to perform processing of substrates charged on a boat in a reaction furnace comprising a reaction tube, a heater to heat the inside of the reaction tube, and a furnace port located below the heater and including metal parts which support the reaction tube, and the substrate processing apparatus includes a controller to control to repeat a step of coating a plurality of times, in which a film is coated on the surface of metal parts, while supplying gas to be used for substrate processing, into the reaction furnace before the substrate processing. Work of repeating the coating step a plurality of times before the substrate processing can be performed easily with a simple structure of having a control apparatus.